Ok, hopefully a simple question for you guys, but I am getting really worried that this is going to turn out bad for me...

I had my tranny rebuilt a few months ago. When I finally got the car back, I noticed a very distinct gear whine that was perfectly linear to the speed of the car, and never changed pitch with gear change, so I immediately concluded it was something with the differential in the tranny. Over time though, it has gotten much louder and noticably worse. This last weekend, I changed the diff fluid, and let me tell you, there was enough metal gook on the magnetic drain plug to make a smal snowman. Any idea why this would happen? I imagine that the diff can't be easy to mess up seeing that it can only really fit in one way.

Also, anyone ever have to change one of these? does it requre the whole tranny being pulled out, or can it be done through the bottom?

Anyone who can help, please!